JP2714271B2 - Cordless telephone equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cordless telephone device capable of reducing not only noise entering from a radio unit but also other noises such as white noise.

[0002]

2. Description of the Related Art A cordless telephone device is a telephone device in which a telephone device main unit and a slave unit are wirelessly connected to each other, and an audio signal from a partner is converted into an audio signal compression circuit (compander IC) in the telephone device main unit. , And then modulated by a frequency modulation circuit, amplified by an amplifier circuit, and transmitted from an antenna. Then, the transmitted signal is input to the tuner section via the slave unit's antenna, demodulated there, expanded by an audio signal expansion circuit (compander IC), and further amplified by an amplifier circuit. Sound is generated from a speaker connected to the amplifier circuit. On the other hand, the own voice input from the microphone of the slave unit is subjected to the above-described level compression, modulation / amplification processing, and the like, transmitted to the telephone device main unit, and transmitted from the telephone device main unit to the other party. Will be.

As described above, in the cordless telephone apparatus, the level compression processing is performed before transmitting the audio signal by using the above-mentioned compander (compressor / expander) IC, and the expansion processing is performed to the original level after the reception. To reduce the noise coming from the wireless unit (Japanese Patent Publication No. 51-4800).
No. 8).

[0004]

However, in the above-described conventional configuration, the noise coming from the radio section is reduced simply by compressing / expanding the signal level. Has the disadvantage that some of them cannot be removed. For example, low-level white noise inherently present, minute noise that can be heard as a side tone due to ambient noise coming from the mouthpiece of your handset when there is no sound, ambient noise coming from the other handset when there is no sound, fluorescent light Noise and noise generated from computer equipment cannot be sufficiently removed.

An object of the present invention is to provide a cordless telephone apparatus which is quieter and has higher sound quality by removing the noise which cannot be completely removed by compression / expansion of the signal level.

[0006]

According to the present invention, there is provided a cordless telephone apparatus for transmitting and receiving a voice signal using a high-frequency carrier wave. A compression section for compressing the signal, a modulation transmission section for modulating the compressed signal passed through the compression section and transmitting the modulated signal are provided, while a reception section includes a demodulation section for demodulating the received signal, and a level conversion section for demodulating the demodulated signal. It is characterized in that it is provided with an expansion section for expanding and an attenuation processing means for attenuating a high-frequency component signal having a low signal level among the expanded signals.

[0007]

According to the above construction, the level compression / expansion processing reduces the noise entering from the radio section, and attenuates the signal of the high-frequency portion of the signal having a low level. Therefore, it is possible to further reduce noise coming from the wireless unit and noise such as white noise.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing a configuration of a slave unit 100 of the cordless telephone device according to the present invention. The handset 100 includes an antenna 5 for transmitting and receiving radio waves, and includes a hand microphone 1, an audio signal compression circuit 2 connected to the hand microphone 1, and an audio signal compression circuit 2 connected to the audio signal compression circuit 2 in a transmission side function unit. A frequency modulating circuit 3 and an amplifying circuit 4 connected to the frequency modulating circuit 3, and a tuner 6 connected to the antenna 5 and a sound connected to the tuner 6 A signal expansion circuit 7, a noise reduction circuit 8 connected to the audio signal expansion circuit 7, an amplification circuit 9 connected to the noise reduction circuit 8, and a speaker 10 connected to the amplification circuit 9 are provided. I have.

Audio signal compression circuit 2 and audio signal decompression circuit 7
As shown in FIG. 2, the main part is incorporated in one compander IC (for example, NE575 provided by Significants) can be used, and a resistor, a capacitor, etc. provided around the compander IC 11 can be used. When the reference value of the audio signal level is set in the operational amplifier and the signal is lower than the reference value, the level is compressed at a fixed ratio, and vice versa. The level is extended by setting.

The compression / expansion characteristics of the compander IC 11 are as shown in the graph of FIG. 3. According to this graph, for example, when a noise of −25 dB is added to a compressed signal, the noise becomes − after expansion. It is reduced to 50 dB. As shown in FIG. 4, the noise reduction circuit 8 includes a noise reduction processor (for example, NEW JAPAN).
NJRC LIN provided by RADIO Co, LTD
EAR IC; NJM 2063A can be used) and electrical elements such as resistors and capacitors provided in the periphery thereof, including two completely separate noise reduction circuit portions, and both encoding and decoding modes. , But are connected so that only the decoding side is used.

The noise reduction characteristic of the noise reduction processor 12 is as shown in the graph of FIG. 5. According to this graph, the noise reduction characteristic has a characteristic that the degree of attenuation varies depending on the level and frequency of the input signal. I understand. According to the above configuration, when noise of −20 dB is added to the compressed signal, the noise included in the signal that has passed through the audio signal decompression circuit 7 is reduced to −40 dB, and the noise of −40 dB is, for example, the frequency Is about 4000
For those above Hz, it is further attenuated to about -50 dB.

Here, when only noise reduction by the noise reduction circuit 8 is performed without performing compression / decompression processing, noise of -20 dB (about 4000 Hz or more) is used.
Is only attenuated to about -30 dB. When only the compression / expansion processing is performed and the noise reduction processing by the circuit 8 is not performed, the noise of -20 dB is attenuated by only about -40 dB. Therefore, it can be seen that the level reduction ability of the configuration of the present invention is the largest.

The compression by the compander IC 11
The only noise that is attenuated by the expansion is the noise that enters from the wireless unit, and white noise, ambient noise that enters from the mouthpiece, and the like remain in the expanded signal without being attenuated. The high-frequency signal of the expanded signal passes through the noise reduction circuit 8 and is attenuated to a different extent depending on its input level. That is,
The lower the input level, the greater the attenuation.
Here, since the input noise belongs to a signal having a low input level, the input noise is greatly attenuated compared to the input audio signal, and a noise reduction effect can be obtained also for white noise and the like existing in a high frequency part. become.

Further, as described above, in this embodiment, the noise reduction processor 12 which performs both the encoding and decoding functions to obtain the original noise reduction effect uses only the decoding function. Therefore, the noise coming from the radio unit is further reduced and the white noise and the like are reduced. Thus, since the existing noise reduction processor 12 is used as the noise reduction circuit 8, the noise reduction is performed. The circuit 8 also has an effect that an inexpensive cordless telephone device can be provided by avoiding an increase in price due to an increase in cost due to a new circuit assembled and manufactured.

[0015]

As described above, according to the present invention, not only noise coming from the radio unit but also other noise (high-frequency noise) such as white noise is reduced, so that the call quality in the cordless telephone device is improved. It has the effect of being able to. Further, after the received signal is expanded, the high-frequency portion is attenuated for a signal having a low signal level, so that the noise can be significantly suppressed as the signal approaches a no-signal. Further, when the signal level is large, the attenuating process is not performed, so that there is no influence of the attenuation on the signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a slave unit of a cordless telephone device as one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a compander IC and the like constituting an audio signal compression circuit and an audio signal decompression circuit.

FIG. 3 is a graph showing compression / expansion characteristics in a compander IC.

FIG. 4 is a circuit diagram showing a noise reduction processor and the like constituting a noise reduction circuit.

FIG. 5 is a graph showing noise reduction characteristics in the noise reduction processor.

[Explanation of symbols]

 2 audio signal compression circuit 7 audio signal decompression circuit 8 noise reduction circuit 11 compander IC 12 noise reduction processor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Masuo Tanaka 2-18-18 Keihanhondori, Moriguchi City, Sanyo Electric Co., Ltd. 56) References JP-A-53-51910 (JP, A) JP-A-63-200633 (JP, A) Tokuyohei 5-502983 (JP, A)

Claims (1)

(57) [Claims] In a cordless telephone device for transmitting and receiving a voice signal using a high-frequency carrier, a transmitting section includes a compression section for level-compressing the voice signal, and a modulation for modulating the compressed signal passed through the compression section for transmission. The transmitting section is provided, while the receiving section includes a demodulating section for demodulating a received signal, an extending section for extending the level of the demodulated signal, and a signal of a high-frequency component of the expanded signal. A cordless telephone device comprising: attenuation processing means for performing attenuation processing on a low-level telephone.